Manufacture of lithopone



Gct. 1l, 1932.

A E. J. FLYNN MANUFACTURE OF LITHOPONE Filed Aug. '7. 1928" INVENTOR Edmund j ,fC/0722 mi y Patented Oct. 11, 1932 narra- A :gaaanz EBMUND J. FLYNN, OF iPALll/IERTON, lIl?ENNSYIANIA, ASSIGNOR TO THE NEW' JERSEY i ZNC COMPANY, OF NEW' vYORK, N. Y., .A CORPORATON 0F NEW'JERSEY" VMANUIAC'IURE 0F LITHOPONE Application led August 7, 1828. Serial No. 297,949. y

This invention relates to the manufacture of lithopone andl has for its object the provision 'of ,certain improvements in lithopone manufacture. More particularly, 'the inventionaims to providefor the precipitationof crude lithopone under substantially uniform conditions.

` Crude lithopone pared by mixing solutions of zinc sulfate and barium sulfide. The resulting white precipitate constitutes what is known in the art as crude lithopone. It has heretofore beenthe customary-practice to carry out this precipiationas a batch operation. Thus, it has been customary to first introduce a predetermined quantity` of the purified zinc sulfate solution or liquor into the precipitating tank. `A predetermined quantity of .the purified barium sulide'solution or liquor is then'gradually added to the precipitating tank, and the two solutions intimately mixed with a resultant precipitation of crude lithopone.y

the balance water with the gradual additionl` thereto of a solution containing 12% barium sulfide and the balance water, it is clear that as thepr'ecipitation of orudelithopone proceeds and the barium and zinc salts are removed from solution, the water previouslyassociated with these salts progressively dilutes the remaining zinc short, precipitation starts in a rather concentrated solution of zinc sulfate and ends in a very dilute solution of zinesuifate.

Microscopic examination of the crude lith- Vopone precipitated in this heretofore customary manner shows that the lithopone is manufactured or pre- For sulfate solution. In Y particlesV to various sizes of aggregates, that lis, aggregates containing lvarying numbers of primary particles.- I have discovered that important advantages, Vboth with respect to product and process, may be obtained by carrying outfthe'precipitationof the crude lithopone under substantially constant or uniform conditions ofliquor concentrations, hydrogen ion concentration, pulp density, temperature, agitation, etc. I have found that these uniform conditions caribe established and maintainedby appropriately controlled `continuous precipitationof the crude lithopone, as distinguished from the heretofore customary batch operations.

The present invention thus consists in causing the barium sulfide and zinc sulfate liquors to flow concurrently and at substantially constant predetermined rates into a mixing or precipitation tank from which such an amount ofthe contents (crude lithopone pulp) is continuously withdrawn as to maintain a substantially constant volume of crude lithopone pulp in the tank. After having fixed the rate of withdrawal and the rate Y of agitation, the various aforementioned conditions within t-he precipitating tank r-emain substantially constant provided of` course that a predetermined uniform supply of each of the precipitating liquors is maintained. Precipitation of the crude lthopone under uniform conditions is thus achieved.

If the barium and zinc solutions enter the precipitation tank at substantialiy the same point,` precipitation of the crude` lithoponeV occurs in practically the' original concentration of these solutions. vlf, however, the Zinc v sulfate solution enters the precipitation tank at some distance from the barium sulfide solution, the zinc solution is diluted by the mother liquor of the pulp as it is swept around by the agitator to meet the incoming barium solution. The precipitation therefore takes place with a Zinc sulfate solution more dilute than the original. By thus varying the distance between the points at Vwhich the barium and Zinc'solutions are introduced into the precipitating tank, precipitation of the crude lithopone can be effected Vunder In plant practice of the invention, *theV .e mixing of the barium and zinc'solutions and the jprecipitation of the crude lithopone take place continuously inone tank. yCrude lithopone pulp is continuously withdrawn from this mixing and precipitating ,tank at suchv` a rate as to maintain a substantially constant liquid level in the tankq The 4pulp vthus withdrawn from the mixing andpreoipitatingtank is pumped or otherwise appropriately yconveyed to one ormore finishing tanks. rEhe-'finishing tanks may be operated in' a continuous manner, similar to the main reaction' or precipitating tank, or the finishing maybe carriedV out-asa batch-operation'. In either case, the small additional quantity of barium sulfide :liquor necessary to reach the ,desired predeterminedfendpoint of the precipitating reaction is' added to the Y.

finishingtank. `In the course of the finishing operation-the crude lithopone pulp'is agitated 'for about two to three hoursthen thickenedv and'k filter-pressed in the customary manner. Practically vall of the crude lithopone is precipitated in the first tank bythe process of continuous precipitation. rIlh'e remaining tanks are'essentially for the purpose Vof balancing'and adjusting the end-point of the precipitation. Fig. lis of the accompanying drawings diagrannnatically illustrates an arrangement of apparatus adapted for the practicey ofthe invention',

il Fig. 2 is a diagrammatic illustration of a modified arrangement of the finishingtank,

, and r A Y n 1 Fig. 3`is a diagrammatic plan view of the main reaction or precipitating tank.

Y The apparatusillustrated inV Fig. 1 of the drawings comprises a storageand supplytank 5 for the purified zinc Vsulfate liquor anda storage and supplytank 6 for the purified barium sulfide liquor; The main reaction or mixing-tank 7 is positioned below vthe storage tanks 5 and 6 andl is provided'withv al rotatable paddle agitator .8. The finishing, tanks 9 and 10 lare at respectively lower levels than the tank 7 and each is provided with a rotary agitator8. f v Y The barium sulfide liquor flows from the Itank 6 to a pipe line 11 having valve-controlled branches 12, 13 and 14 for'vfeeding barium sulfide liquor to thetanks 7, 9 and '10 respectively.' Similarly, thel tanks`7, 9

Aand 10 are adapted to receive zinc sulfate liquor through valve-controlled branches v15, .116 and 17, respectively, of a pipeline 18 leading from the tank 5, l n

As shown in Fig.V 3, the branch' pipe 12 is relatively stationary, whereas the branchkr pipeV 15 is movable about the inner periphery of the tank 7, whereby the zinc sulfate liquor may be introduced into vthe tank 7 at any desired point around the inner periphery thereof. llnYFig.. 3 of the drawings four illustrative positions of the pipe 15 areindicated by reference numerals 15, 15a, 15b and 150. Y Zinc sulfateliquorV flows'v continuously through the branch 'pipe 12 linto lthe main with thel first finishing tank 9; In the tank 9, the crude lithopone pulp is continuously agitated and mixedv by the rotating paddle stirrer 8. -Appropriate small kamountsfof barium sulde liquor are introduced into-the tank through the branch 13 until the desired endpoint is reachedor closely approximated. Y

Cude pulp 1 is continuously withdrawn-*by gravity fromthe tank-9 through an uptake well 19 into an overflow launder'QOFconnesting with the secondfinishing ftank" 10. In the tank 10 the crude pulp isfsubjected to thesame finishing treatment as in the tank 9i, and the endpointo the Aprecipitating reaction is definitely and accurately controlled;

Y `From thetank 10, the crude litliopone pulp is lwithdrawn by gravity through an uptake well 19l into an overflow launder20-'and loo conveyed to settling or .thickening j tanks. l

Y The thickenedpulp'is then filtered in accordance'withithe heretofore customary practice. Theidesir'ed endpoint of the precipitating re- -action'will ordinarily be obtained inthe'finishing tanks V9 and Y10 ,by the addition thereto of small amounts of barium sulfide liquor'. Provision is made, however, for the introduci tion of zinc s idfatey liquor to the tanks9 and 10, in the event that this is desirable or necessary Vin the nishing operation.

A slightly modified arrangement ofthe finishing tanks is illustrated in 'Fig 2V of the drawing. inthe arrangement of Fig. 1, the

various tanks are positioned. at respectively difi-erent levels, andthe fiow of the pulp from Y the main reaction tank to and through the A'finishing tanks 1s effected by gravity. In the arrangement of Fig. 2, the main reaction tank and the finishing tanks are positioned at substantially the same level.` lt is there- .fore necessary to pump or otherwise mechanically withdraw the 'pulp' vfrom each tank. YTo this end,-the main reaction ltank 7isipifo.- vided withan outlet pipe 21 having itslower A tionand zinc sulfate solution into the tank l Cil Vbarium sulfide.

or inlet end near the bottom of the tank. The top ofthe pipe 2l connects with-a steam ej ecs tor22 having a'valve-controlled steam supply pipe 23. Pulp is withdrawn from the main reaction tank by the ejector 22 and introduced into a finishing tank 24; ln accordance with the principles of theA present invention, the rates of introduction of barium suliide soluand the rate of withdrawal otpulp from this tank are so `regulated as to maintain the liquor concentrations kci the pulp in the tank substantially consta-nt; j y .v

The finishing tank 2l has a valve controlled outlet 25 in the bottom thereof connected to a pump 26. When the tank 2lihasbeen substantially filled with crude pulp withdrawn from the tank i', itis iinished ofi in substantially Athe lmanner heretofore customary in batch operations. y ln the meantime, the pulp withdrawn from' the tank 7 is introduced into another finishing tank. From the finishing tanks 24 the crude lithopone pulp is conveyed to settlers,thickeners, storage tanks or the like, and subsequently to iilters in the heretoore'customary manner. Y

lVhen the barium sulfide and Zinc sulfate supply pipes occupy the. positions representedby reference numerals l2l and l5 of F ig. 3, the zinc sulfate solution comes into contact with the barium sulfide solution almost immediately, without having had an opportunity ot becoming appreciably diluted or dispersed vby adinixture with thev precipitate slurry or crude `lithopone pulp. Precipitation takes place in concentrations of solutions closely approaching those existing in the supply tanks 5 and 6. Underlthese 'conditions the crude lithopone settles more rapidly and has a higher hiding power than crude lithopone made by the heretofore 'customary batch operation. ln the process of the invention, the ultimate particles oi"- the crude lithopone are inV uniformly sized aggregates, whereas in the batch operation the crude lithopone contains aggregates made lup of widely varying numbers of particles. The calcined product, made in accordance withthe invention,is soft and possesses unusually high hiding power, and when made into paint is exceptionally smooth and glossy.

l/Vhen the zinc sulfate solution enters the tank i' at the point indicated by reference numeral l5@ of 3, there is considerable `opportunity Jfor it to be diluted and dispersed by admixturewith thev crude lithopone pulp before the agitator swirlcarries it around toV the point where it comes into Acontact with ln this case precipitation takes pace inve'ry much more dilute solutions than when the zinc sulfate liquor enters vat 15. `Yihen precipitated under these conditions, the crude lithopone settles even more nra idl and has even hi 'herhidineL newer than'when' the Zinc sulfate liquor ent-ers at 15. The ultimate particles of the crude litho- Vpone are uniformlyaggregated as before, but

Throughout this specification and the appendedl claims, l have Vused the expression -liquor concentrations to designatcthe concentrations oi barium sulfide, Zinc sulfate and other `water-soluble compounds in the liquor or medium in which. the barium sulfide and zinc sulfate are. brought into reactiverelations with one another.l l/Vhile I prefer that this medium shall consist `of' a substantial body/of crude lithopone pulp, wide variations in the volume of this body ofpulp are permissible without departing` from the principles ofthe invention.

The following advantageous results are obtained'k by the practice of the present inventions'.V y v 'l l. A precipitate slurry orcrude lithopone pulp in which the. lithopone particles exist ina much more/uniform state ot aggregation than in theheretofore customary batch operation. .Single particles and very Vlarge aggregates otparticles are substantially absent. 'On .the other hand,.the relative size of the aggregatesv mayfbe varied by varying theliquor concentrations in whichprecipi'- tation occurs either by diluting the original -reactingjliquors orbyvarying the relative spacing-of the streams of barium and zinc solutions entering the precipitation tank.` 2. A. precipitate slurryin-which the lithopone settles more rapidly than in theheretofore customary batch practice, lilters more readily, and results in a. lithopoiielter-cake of decidedly lower characteristic maybe 'varied to some extent by varying the liquor concentrations in the precipitation stage. I :l

i 8.1i dried' lcrude lithopone of ay compara-` tively chalky,' soft'charact'er, in contrast-.to the-rather hard crude lithopone ofthe batch operation. i y l produced inthe batch operation. rlhis vpermits theiproduction with'fa decidedly lesser amount of'grinding or wet millingof a lithomoisture content.V 'This' poncequal to that of the batch operation, and with equal grinding. a finished lithopone of decidedlyY softer and smoother texture.

6. An ultimate lithopone product equal and in general superior to that produced by the batchl operation in hiding power, color, brightness and smoothness. Furthermore, an ultimate lithopone product with a superior uniformity of size of' aggregates, which is probably responsible for the superiority of the product in the aforementioned character.- i

istics, particularly smoothness.

I claim s s l. In the manufacture of lithopone the method of'producing crude lithoponeof high quality which consists in continuously running aqueous solutions of zinc sulphate and of barium sulphide in reactive proportions into a precipitating and mixing tank, energetically stirring the contents of said tank, continuously drawingofi' the contents of said tankin such manner as to maintain an approximately constant `levelgtherein and -approximately constant concentration of the liquid. contents thereof and. settling out a lithopone pulp from the mixture drawn from the tank.

2. In "the method of claim 1 Vthe further step of continuously passing the mixture from the precipitating and mixing tank through one orV more similar precipitating and mixingtanks prior to settling out the pulp so as toinsure a complete reaction.

of continuous agitation adapted to provide a substantially complete reaction between the Zinc sulfate and barium sulfide liquors, and continuously overfiowing slurry from the relaction chamber, said slurry being withdrawnfrom the reaction chamber at or near the opposite end at which the reacting liquors vare first introduced into the. chamber.

4. kThe improvement in the manufactureY .of' lithopone which comprises introducing `simultaneously and continuously aqueous solutions of zinc sulfate and barium sulfide in a reaction chamber, providing a crude lithopone slurry inthe reaction chamber having a liquor concentration adapted to promote the 'formation of substantially v,uniformly sizedraggregates of tbeultimate lithopone particles, then maintaining said' slurry of crude lithopone'at said predetermined liquor lconcentration in the chamber as further amounts ofzinc sulfate and barium sulfide solution are brought-into reactive relation, and continuously withdrawing regulated amounts of slurry from said reaction chamber.-

, 5. The improvement in themanufacture oflithopone which comprises continuouslyA introducing bariumsulfide solution and zinc sulfatesolutioninto a body of crude lithopone pulp,continuously withdrawing pulpl fromsaid body thereof, and regulating the rates of-introduction-of said solutions and the rate of withdrawal of said 'pulp sofas to maintain the liquor concentrations of saidbody of vpulp substantially constant, said liquor. concentrations being adapted to promote the formation of substantially uniformly sized aggregates of the ultimate lithopone particles. Y

6. The improvementintlie manufacture` of lithopone which comprises continuously introducingbarium sulfide solution and zinc sulfate solution-into a body of crude lithopone pulp ofV substantially constant liquor concentrations, the point of introduction `of said solutions into the pulp being so spaced as tobring'thebariuni sulfide and Zinc sulfate into reactive relation with one another at predeterminedV ,Y liquorV concentrations .adapted to promotethe forniationof sub.-

stantially uniformly 'sized aggregates .of .the ultimateV lithopone particles. Y s s y' Y 7 The improvement in the manufacture of lithopone which comprises continuously introducing barium sulfide solution and zinc sulfate solution concurrently into a bodyof crude lithopone pulp, and continuously maintaining the liquor concentrations of said body of pulp substantially constant, saidliquor concentrations being adapted to Apromote the formationv of substantially uniformly sizedaggregates of the ultimate lithopone particles. l

8. `The improvement inthe manufacture of lithopone which comprises concurrently introducing barium sulfide solution and Zinc sulfate solution into a body of crude lithopone` pulp of substantially constant liquor concentrations, saidliquor concentrations being adapted to promote the formation of substantially uniformly sized aggregates of the ultimate lithopone particles. 4 K y 9. The improvement in the manufacture of lithopone which kcomprises simultaneously and continuously introducing solutions of .i

zinc sulfate and barium sulfide intoa reaction chamber, regulating the flow of the solutions of zinc sulfate and'barium sulfide into the reaction chamber., so as to provide and kmaintain a lslurry of crude lithoponeof substantially unchanging liquorf concentrations, continuously withdrawing crude lithopone slurry from the reaction chamber and treating the crude lithopone slurry so Withdrawn with the reacting solutions to obtain a predetermined endpoint of the precipitation reaction.

10. The improvement in the manufacture of lithopone which comprises simultaneously and continuously introducing solutions of Zinc sulfate and barium sulde into a reaction chamber, regulating the flow of the solutions of zinc sulfate and barium sulfide into the reaction chamber, so as to provide and maintain a slurry of crude lithopone of substantially unchanging liquor concentrations, continuously withdrawing crude lithopone slurry from the reaction chamber and treating thecrude lithopone slurry so withdrawn to obtain a predetermined end point ofthe precipitation reaction.

l1. The improvement in the manufacture of lithopone which comprises simultaneously and continuously introducing solutionsof zinc sulfate and barium sulfide into a reaction chamber, regulating the flow of the sotreating the resulting lithopone slurry to 'obtain a predetermined end point of the precipitation reaction.

15. The improvement in the manufacture of lithopone which comprises continuouslyr introducing barium sullide'solution and zinc sulfate solution intov a body of crude lithopone pulp, continuously withdrawing Vpulp from said body thereof, and regulating the rates of introduction of said solutions and the rate of withdrawal of said pulp so as to lutions of Zinc sulfate and barium sulfide into v the reaction chamber, so as to provide and maintain a slurry of crude lithopone of substantially unchanging liquor concentrations, continuously withdrawing crude lithopone slurry from the reaction chamber to a finishing tank, treating the crude lithopone slurry in the finishing tank to obtaina predetermined end pointof the precipitation reaction, and continuously withdrawing treatedV crude lithopone slurry from the finishing tank.

12. The improvement in the manufacture of lithopone which comprises simultaneously and continuously introducing solutions of zinc sulfate and barium sulfide into a miX- ing and precipitation tank, continuously withdrawing crude lithopone slurry Yfrom the mixing and precipitation tank, and treating the crude lithopone slurry so withdrawn to obtain a predetermined end point of the precipitation reaction.

13. The improvement in the manufacture of lithopone which comprises concurrently introducing solutions of barium sulfide and zinc sulfate into reactive relation with one another in a mediuml of substantially unchanging liquor concentrations, and then treating the resulting crude lithopone slurry to obtain a predetermined end point of the precipitation reaction.

14. The improvement in the manufacture of lithopone which comprises continuously introducing barium sulfide solution and zinc sulfate solution into a body of crude lithopone pulp of substantially constant liquor concentrations, the points of introduction of said solutions into the pulp being so spaced as to bring the barium sulfide and zinc sulfate into reactive relation with one another at predetermined liquor concentrations, and

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